This application claims the benefit of Japanese Application No. 2001-308133 filed Oct. 4, 2001.
The present invention relates to a water/fat phase identifying method, image producing method and magnetic resonance imaging apparatus, and particularly to a water/fat phase identifying method for identifying the phases of water and fat in a complex image captured using magnetic resonance, an image producing method for producing a water image or a fat image, and a magnetic resonance imaging apparatus for suitably implementing these methods.
Japanese Patent Application Laid Open No. 2001-204711 discloses a method involving: capturing a complex image using magnetic resonance with the phase differentiated between water and fat; extracting separate signal regions in the complex image; generating respective phase histograms of the signal regions; and identifying the phases of water and fat based on the phase histograms.
The conventional technique disclosed in Japanese Patent Application Laid Open No. 2001-204711 conducts processing for extracting separate signal regions in a complex image.
The area of the signal region, however, varies because it depends on the image. If the area of the signal region is too small, the number of data points contained in the signal region is too small and the effect of noise becomes significant, whereby a good phase histogram cannot be obtained. On the contrary, if the area of the signal region is too large, the effect of inhomogeneity of the static magnetic field becomes significant, and again, a good phase histogram cannot be obtained. If a good phase histogram cannot be obtained, the phases of water and fat cannot be suitably identified.
It is therefore an object of the present invention to provide a water/fat phase identifying method capable of suitably identifying the phases of water and fat without conducting the processing of extracting separate signal regions in a complex image, an image producing method for producing a water image or a fat image, and a magnetic resonance imaging apparatus for suitably implementing these methods.
In accordance with its first aspect, the present invention provides a water/fat phase identifying method characterized in comprising: capturing a complex image using magnetic resonance with the phase differentiated between water and fat; dividing said complex image into a multiplicity of sections; generating a phase histogram for each section; determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; if the phases cannot be identified, generating an additive phase histogram by adding phase histograms of sections in a predefined range proximate to the section of interest; and obtaining the phases of water and fat in the section of interest from said additive phase histogram.
In the water/fat phase identifying method of the first aspect, a complex image is divided into a multiplicity of sections; if the phases of water and fat can be identified from a phase histogram of a certain section, the phases of water and fat are obtained from the phase histogram of the section; and if the phases cannot be identified, phase histograms of proximate sections in a predefined range are added to obtain the phases of water and fat from an additive phase histogram. Since the area for which a phase histogram is generated is thus automatically changed, the phases of water and fat can be suitably identified.
In accordance with its second aspect, the present invention provides a water/fat phase identifying method characterized in comprising: capturing a complex image using magnetic resonance with the phase differentiated between water and fat; dividing said complex image into a multiplicity of sections; generating a phase histogram for each section; determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; if the phases cannot be identified, generating an additive phase histogram by adding phase histograms of sections in a predefined range proximate to the section of interest; determining whether the phases of water and fat can be identified from said additive phase histogram; if the phases can be identified, obtaining the phases of water and fat in the section of interest from said additive phase histogram; and if the phases cannot be identified, repeating the foregoing processing with stepwise enlargement of said predefined range to obtain the phases of water and fat in the section of interest.
In the water/fat phase identifying method of the second aspect, a complex image is divided into a multiplicity of sections; if the phases of water and fat can be identified from a phase histogram of a certain section, the phases of water and fat are obtained from the phase histogram of the section; and if the phases cannot be identified, phase histograms of proximate sections in a predefined range are added; if the phases of water and fat can be identified from the additive phase histogram, the phases of water and fat are obtained from the additive phase histogram; and if the phases cannot be identified, the same processing is repeated with stepwise enlargement of the predefined range. Since the area for which a phase histogram is generated is thus automatically changed, the phases of water and fat can be suitably identified.
In accordance with its third aspect, the present invention provides the water/fat phase identifying method having the aforementioned configuration, characterized in comprising: if the phases cannot be identified even when said predefined range is enlarged to a predefined limit range, terminating said repetition of the processing, and obtaining the phases of water and fat in the section of interest based on phases of water and fat of another section whose phases of water and fat could be obtained.
In the water/fat phase identifying method of the third aspect, the enlargement of the area for which a phase histogram is generated is terminated at a predefined limit range, and the phases of water and fat in a section of interest are obtained based on phases of water and fat of another section whose phases of water and fat could be obtained. This prevents unnecessarily lengthening of the processing time.
In accordance with its fourth aspect, the present invention provides the water/fat phase identifying method having the aforementioned configuration, characterized in that: when enlarged for an i-th (i=1, 2, . . . ) time, said predefined range is an range which has the section of interest surrounded by i layers of other sections.
In the water/fat phase identifying method of the fourth aspect, since the area for which a phase histogram is generated is enlarged so that a section of interest is surrounded by other sections, the section of interest is centered, and any first-order phase shift between the sections can be canceled out.
In accordance with its fifth aspect, the present invention provides a water/fat phase identifying method characterized in comprising: capturing a complex image using magnetic resonance with the phase differentiated between water and fat; dividing said complex image into a multiplicity of sections; generating a phase histogram for each section; determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; and if the phases cannot be identified, obtaining the phases of water and fat in the section of interest based on phases of water and fat of a section which lies proximate to the section of interest and whose phases of water and fat could be obtained.
In the water/fat phase identifying method of the fifth aspect, a complex image is divided into a multiplicity of sections; if the phases of water and fat can be identified from a phase histogram of a certain section, the phases of water and fat are obtained from the phase histogram of the section; and if the phases cannot be identified, the phases of water and fat in the section of interest are obtained based on phases of water and fat of another section whose phases of water and fat could be obtained. This reduces the processing time.
In accordance with its sixth aspect, the present invention provides the water/fat phase identifying method having the aforementioned configuration, characterized in that: said complex image is divided to form a grid.
In the water/fat phase identifying method of the sixth aspect, since the complex imaged is automatically divided, no image analysis is needed and the processing time is reduced.
In accordance with its seventh aspect, the present invention provides the water/fat phase identifying method having the aforementioned configuration, characterized in that: said complex image is divided so that from 64 to 4,096 data points are contained in each section.
In the water/fat phase identifying method of the seventh aspect, since the complex image is divided so that from 64 to 4,096 data points are contained in each section, the area for which the phase histogram is generated is never too small or too large.
In accordance with its eighth aspect, the present invention provides an image producing method characterized in comprising: capturing a complex image using magnetic resonance with the phase differentiated by 90xc2x0 between water and fat; dividing said complex image into a multiplicity of sections; obtaining the phase of water in each section; and acquiring a water image from the real part of the complex image after subtracting from each data point in said complex image the phase of water in the corresponding section.
In the water/fat phase identifying method of the eighth aspect, since, from each data point in a complex image, the phase of water in the corresponding section is subtracted, the phase of water is xe2x80x9c0xe2x80x9d. Therefore, the real part of the complex image after the subtraction provides a water image.
In accordance with its ninth aspect, the present invention provides an image producing method characterized in comprising: capturing a complex image using magnetic resonance with the phase differentiated by 90xc2x0 between water and fat; dividing said complex image into a multiplicity of sections; obtaining the phase of water in each section; and acquiring a fat image from the imaginary part of the complex image after subtracting from each data point in said complex image the phase of water in the corresponding section.
In the water/fat phase identifying method of the ninth aspect, since, from each data point in a complex image, the phase of water in the corresponding section is subtracted, the phase of fat is xe2x80x9c90xc2x0xe2x80x9d. Therefore, the imaginary part of the complex image after the subtraction provides a fat image.
In accordance with its tenth aspect, the present invention provides a magnetic resonance imaging apparatus characterized in comprising: image capturing means for capturing a complex image using magnetic resonance with the phase differentiated between water and fat; histogram calculating means for dividing said complex image into a multiplicity of sections, and generating a phase histogram for each section; first determining means for determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; first phase obtaining means for, if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; additive phase histogram generating means for, if the phases cannot be identified, generating an additive phase histogram by adding phase histograms of sections in a predefined range proximate to the section of interest; and second phase obtaining means for obtaining the phases of water and fat from said additive phase histogram.
In the magnetic resonance imaging apparatus of the tenth aspect, the water/fat phase identifying method of the first aspect can be suitably implemented.
In accordance with its eleventh aspect, the present invention provides a magnetic resonance imaging apparatus characterized in comprising: image capturing means for capturing a complex image using magnetic resonance with the phase differentiated between water and fat; histogram calculating means for dividing said complex image into a multiplicity of sections, and generating a phase histogram for each section; first determining means for determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; first phase obtaining means for, if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; additive phase histogram generating means for, if the phases cannot be identified, generating an additive phase histogram by adding phase histograms of sections in a predefined range proximate to the section of interest; second determining means for determining whether the phases of water and fat can be identified from said phase histogram; second phase obtaining means for, if the phases can be identified, obtaining the phases of water and fat in the section of interest from said additive phase histogram; and repeating means for, if the phases cannot be identified, repeating the foregoing processing with stepwise enlargement of said predefined range to obtain the phases of water and fat in the section of interest.
In the magnetic resonance imaging apparatus of the eleventh aspect, the water/fat phase identifying method of the second aspect can be suitably implemented.
In accordance with its twelfth aspect, the present invention provides the magnetic resonance imaging apparatus having the aforementioned configuration, characterized in that: if the phases cannot be identified even when said predefined range is enlarged to the limit range, said repeating means terminates said repetition of the processing; and said magnetic resonance imaging apparatus comprises third phase obtaining means for obtaining the phases of water and fat in the section of interest based on phases of water and fat of another section whose phases of water and fat could be obtained.
In the magnetic resonance imaging apparatus of the twelfth aspect, the water/fat phase identifying method of the third aspect can be suitably implemented.
In accordance with its thirteenth aspect, the present invention provides the magnetic resonance imaging apparatus having the aforementioned configuration, characterized in that: when enlarged for an i-th (i=1, 2, . . . ) time, said predefined range is an range which has the section of interest surrounded by i layers of other sections.
In the magnetic resonance imaging apparatus of the thirteenth aspect, the water/fat phase identifying method of the fourth aspect can be suitably implemented.
In accordance with its fourteenth aspect, the present invention provides a magnetic resonance imaging apparatus characterized in comprising: image capturing means for capturing a complex image using magnetic resonance with the phase differentiated between water and fat; histogram calculating means for dividing said complex image into a multiplicity of sections, and generating a phase histogram for each section; first determining means for determining whether the phases of water and fat can be identified from the phase histogram of a section of interest; first phase obtaining means for, if the phases can be identified, obtaining the phases of water and fat in the section of interest from the phase histogram of the section of interest; and third phase obtaining means for, if the phases cannot be identified, obtaining the phases of water and fat in the section of interest based on phases of water and fat of a section which lies proximate to the section of interest and whose phases of water and fat could be obtained.
In the magnetic resonance imaging apparatus of the fourteenth aspect, the water/fat phase identifying method of the fifth aspect can be suitably implemented.
In accordance with its fifteenth aspect, the present invention provides the magnetic resonance imaging apparatus having the aforementioned configuration, characterized in that: said complex image is divided to form a grid.
In the magnetic resonance imaging apparatus of the fifteenth aspect, the water/fat phase identifying method of the sixth aspect can be suitably implemented.
In accordance with its sixteenth aspect, the present invention provides the magnetic resonance imaging apparatus having the aforementioned configuration, characterized in that: said complex image is divided so that 64 or more data points are contained in each section.
In the magnetic resonance imaging apparatus of the sixteenth aspect, the water/fat phase identifying method of the seventh aspect can be suitably implemented.
In accordance with its seventeenth aspect, the present invention provides a magnetic resonance imaging apparatus characterized in comprising: image capturing means for capturing a complex image using magnetic resonance with the phase differentiated by 90xc2x0 between water and fat; phase obtaining means for dividing said complex image into a multiplicity of sections, and obtaining the phase of water in each section; and water image acquiring means for acquiring a water image from the real part of the complex image after subtracting from each data point in said complex image the phase of water in the corresponding section.
In the magnetic resonance imaging apparatus of the seventeenth aspect, the water/fat phase identifying method of the eighth aspect can be suitably implemented.
In accordance with its eighteenth aspect, the present invention provides a magnetic resonance imaging apparatus characterized in comprising: image capturing means for capturing a complex image using magnetic resonance with the phase differentiated by 90xc2x0 between water and fat; phase obtaining means for dividing said complex image into a multiplicity of sections, and obtaining the phase of water in each section; and fat image acquiring means for acquiring a fat image from the imaginary part of the complex image after subtracting from each data point in said complex image the phase of water in the corresponding section.
In the magnetic resonance imaging apparatus of the eighteenth aspect, the water/fat phase identifying method of the ninth aspect can be suitably implemented.
According to the water/fat phase identifying method, image producing method and magnetic resonance imaging apparatus of the present invention, the phases of water and fat can be suitably identified without conducting processing of extracting separate signal regions in a complex image, and a water image or a fat image can be produced.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.